1. Field of the Invention
This invention relates to an apparatus for combining resin bonding and mechanical anchoring of a roof bolt apparatus in a bore hole of a rock formation and more particularly to an expansion assembly having a configuration adapted to facilitate the passage of resin from above the expansion assembly in a bore hole, down past and around the expansion assembly.
2. Description of the Prior Art
It is well known to reinforce and to stabilize underground roof formations, such as a coal mine roof, a subway tunnel or similar subterranean structure or to strengthen a rock mass by the use of anchor bolts inserted within a bore hole drilled in the rock formation. The anchor bolts are tensioned during installation to reinforce the unsupported rock formation above the roof, for example, of a mine passageway. Conventionally, a hole is drilled into the rock formation. The end of the bolt in the rock formation is anchored either by engagement of a mechanical expansion shell with the wall of the rock formation around the bore hole or chemically anchoring the bolt by a multi-component resin system or grout to the rock formation surrounding the bore hole.
The known devices utilize a resin bonding system in conjunction with a mechanical anchor assembly to both chemically and mechanically bond the roof bolt in the bore hole. A disadvantage of this system is that the diameter of the bore hole needed to accommodate the expansion assembly requires excessive amounts of resin, which increases costs significantly.
U.S. Pat. No. 4,764,055 discloses a mine roof bolt expansion assembly for use with resin having a specially configured, thin walled expansion shell together with a dual taper plug for expanding the shell. The shell and plug cooperate to provide a symmetrical array of resin passages at circumferentially spaced locations about the anchor assembly. A rib formation projects from the base of one of the groove like indentations on the outer surface of the plug. The rib projects outwardly into a slot between adjacent leaves or fingers of the shell. In this manner the indentations are aligned with slots in the expansion shell to provide the aforementioned resin flow passageways. Also the ribs serve to prevent unwanted rotation of the plug relative to the shell.
U.S. Pat. No. 2,685,221 discloses a mine roof bolt with a nut-receiving threaded end and a wedge end spaced therefrom having external threads thereon. A split sleeve is threaded onto the wedge end of the bolt and the threads move the wedge end of the bolt into the split sleeve to cause expansion thereof when the bolt is rotated.
U.S. Pat. No. 3,381,567 discloses a roof bolt with a first threaded end for receiving a bearing plate and a second threaded end for receiving a plug thereon for expanding the leaves of an expansion shell. The expansion shell comprises two shell portions which are semi-circular in cross section held around the plug on the second threaded end by a plastic sheath. The shell portions have longitudinally extending slots for receiving opposed fins on the plug to prevent rotation of the plug relative to the expansion assembly.
U.S. Pat. No. 3,941,028 discloses a mine roof bolt with an expansion assembly comprising a plug surrounded by a plurality of fingers extending from an expansion shell. A retainer element maintains the expansion shell in proper position relative to the plug and comprises a stamped element with a threaded bore and extensions which frictionally engage the shell.
U.S. Pat. No. 4,160,614 discloses a mine roof bolt with an expansion shell assembly non-rotatably retained thereon in a given direction by an abutting portion of a clip member and releasably retained thereon by engagement of a releasing portion of the clip member when the bolt is rotated in the opposite direction.
U.S. Pat. No. 4,173,918 discloses a mine roof bolt having a threaded end with an expansion assembly thereon. The expansion shell is prevented from axial movement on the threaded end by a pin extending into a bore subjacent thereto. The expansion assembly has a wedge threadedly engaged to the first threaded end with the expansion shell comprising four leaves separated by slots extending from a base portion thereof. Ribs from the wedge extend into the slots to prevent movement of the plug relative to the shell.
U.S. Pat. No. 4,193,715 discloses a mine roof bolt for use with a resin system comprising a bar and a bolt joined by threaded ends thereof by a coupler. The bar has a shoulder which limits the extension of the threaded end thereof into the threaded coupler. The bar has a pair of nubs with a cylindrical collar positioned thereon between the coupler and the nubs. As the resin is mixed by the bar, it hardens to prevent further rotation of the bolt. Additional torque on the bolt breaks the nubs and/or collar to allow tensioning of the bolt by advancing a bearing plate into tension against the mine roof.
U.S. Pat. Nos. 4,483,645 and 4,534,679 disclose a mine roof bolt comprising a bolt portion with a headed end for securing a bearing plate and a threaded end threadedly received in an axial bore in a rebar portion. An expansion assembly is positioned subjacent the rebar and includes a plurality of expansion leaves connected by reduced neck portions to a base and a cone nut for expanding the leaves of the shell outwardly against the wall of the bore wall. The cone nut may have longitudinal grooves for receiving bail straps of a bail member to prevent rotation of the plug relative to the shell of the expansion assembly.
U.S. Patent No. 31,776 discloses a mine roof bolt having a means for controlling relative rotation between the expansion plug and the mine roof bolt in a given direction.
U.S. Pat. No. 4,611,954 discloses a mine roof bolt having a threaded end and a headed end. An expansion assembly is positioned on the threaded end and comprises an expansion shell with leaves extending toward the terminal end thereof from a base portion of the shell around a plug. The plug has an axial bore for threadedly engaging the threaded end of the mine roof bolt and a deformable plastic ring with an unthreaded bore securely engaged to an end wall of the plug. The threaded end of the plug cuts threads into the plastic ring when resistance to torque on the wedge exceeds the force required to cut the threads in the plastic ring.
U.S. Pat. No. 4,664,561 discloses a mine roof bolt having a threaded end opposite a headed end supporting a bearing plate. A hollow tube having a threaded nut welded to an end thereof is threaded onto the bolt threaded end and a conventional expansion shell plug is connected thereto above the hollow tube. The plug has grooves or channels on opposite sides thereof.
U.S. Pat. No. 4,679,966 discloses a mine roof bolt with a rod having threaded ends connected by a coupler to a bolt having a threaded end opposite a headed end. The threaded end of the rod opposite the coupler has an expansion assembly with a shell and a longitudinally grooved plug with a shear pin extending therethrough. The coupling also has a shear pin extending therethrough.
Canadian Patent No. 751,137 discloses a mine roof bolt with threaded ends spaced from each other by a shaft portion. The bolt has an expansion assembly at one end and a nut retained bearing plate at the other end. The expansion assembly consists of a split shell with a wedge plug for moving the shell into engagement with the wall of the bore hole. A threaded washer on the shoulder of the first threaded end holds the shell in position.
German Patent No. 22 21 267 discloses an expansion assembly with an expansion shell having four leaves axially extending from a base portion around a roof bolt. A wedge plug is threadedly engaged to the roof bolt and a portion thereof extends into the expansion shell. The shell is retained and positioned between the wedge plug and a snap ring which fits into a circular groove in the roof bolt.
A publication by Frazer & Jones entitled "Mine Roof Support Anchors" discloses expansion assemblies comprising plugs with longitudinal grooves therein aligned with slots between the leaves of an expansion shell connected by reduced neck portions to a base portion of the expansion shell.
Another publication by Frazer & Jones entitled "Two Great Names One Great System" discloses expansion shells with reduced neck portions and plugs with grooves therein aligned with the slots between leaves of expansion shells. A dual component resin system in cartridge form for use therewith is also disclosed.
Although the known devices utilize expansion shell assemblies having grooves in plugs aligned with slots between the leaves of an expansion shell, there remains a need for an expansion shell assembly that assures alignment of the grooves with the slots without obstruction of the grooves to the flow of resin in uniform surrounding relation with the expansion shell and in contact with the wall of the bore hole. The alignment of the grooves with the slots must be accomplished efficiently and maintained as the assembled shell and plug is advanced into position for mixing of the resin components and expansion of the shell in the bore hole.